The basic elements of an analog-to-digital conversion system are a digital-to-analog conversion device and a comparator. The comparator detects equality of the input signal with its digitally produced counterpart and a feedback loop adjusts the latter until such equality is obtained. The digital-to-analog device may be resistive in nature, such as a weighted network or R/2R ladder, in which case any output voltage may be maintained indefinitely. Alternatively, the device may utilize a capacitor for storing fixed charge increments. In this case, the finite leakages involved limit voltage maintenance to periods of time, which are nevertheless adequate for many applications. Analog-to-digital converters may be further characterized by output format, which may be a digital word representing the input amplitude, or a pulse representing a defined change in the input amplitude. The present invention is concerned with the design of a practical capacitive storage, tracking analog-to-digital converter for providing the latter format, sometimes referred to as a "delta" format.
Analog-to-digital conversion systems are well known in the electronics field. However, undesirable characteristics inherent in many present day systems include a high component count and circuit complexity, problems stemming from the digitization of small AC signals in the presence of large DC components and difficulties in the multiplexing of input signals.
The present analog-to-digital converter obviates all of the aforementioned problems.